How to draw a thin line regularly across a cylinder
The Simple Deform modifier is what you need!


Create your profile, extrude it, don't keep the faces on the sides.





Give it an Array modifier, enable Merge and First Last options.





Give it a Simple Deform modifier, choose Bend mode and an Angle of 360°.





Continue to build your section the way you want it to be, it will be replicated all around.





Give it a Subdivision Surface modifier, add edge loops to sharpen the edges, etc...